The invention relates to a process for low temperature dehydrogenation of ethane to ethylene and acetic acid in the presence of oxygen, and particularly to a process using a catalyst featuring good conversion and good selectivity.
Low temperature oxydehydrogenation of ethane to ethylene has become well known since the publication of “The Oxidative Dehydrogenation of Ethane over Catalyst Containing Mixed Oxide of Molybdenum and Vanadium” by E. M. Thorsteinson, T. P. Wilson, F. G. Young and P. H. Kasai, Journal of Catalysis 52, pp. 116-132 (1978). This article discloses mixed oxide catalysts containing molybdenum and vanadium together with another transition metal oxide (Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce). The catalysts are active at temperatures as low as 200° C. for the oxydehydrogenation of ethane to ethylene.
The effectiveness of the oxydehydrogenation of ethane to ethylene is usually primarily determined by two parameters: conversion of ethane, and selectivity (efficiency) to ethylene. As used herein, these terms are defined as follows:
            conversion      ⁢                          ⁢      of      ⁢                          ⁢      ethane        =                                        [            CO            ]                    ⁢                      /            2                    ⁢                      +                          [                              CO                2                            ]                                      ⁢                  /          2                ⁢                  +                      [                                          C                2                            ⁢                              H                4                                      ]                                                                          [              CO              ]                        ⁢                          /              2                        ⁢                          +                              [                                  CO                  2                                ]                                              ⁢                      /            2                    ⁢                      +                          [                                                C                  2                                ⁢                                  H                  4                                            ]                                      +                  [                                    C              2                        ⁢                          H              6                                ]                                selectivity      ⁢                          ⁢              (        efficiency        )            ⁢                          ⁢      to      ⁢                          ⁢      ethylene        =                  [                              C            2                    ⁢                      H            4                          ]                                          [            CO            ]                    ⁢                      /            2                    ⁢                      +                          [                              CO                2                            ]                                      ⁢                  /          2                ⁢                  +                      [                                          C                2                            ⁢                              H                4                                      ]                              wherein: [ ]=relative moles of the component and the production of acetic acid is negligible. The terms in the art are sometimes calculated differently but the values calculated either way are substantially the same.
Under certain reaction conditions, substantial amounts of acetic acid can be formed as a co-product and the effectiveness of the reaction to ethylene and acetic acid is calculated by the following equations:
            conversion      ⁢                          ⁢      of      ⁢                          ⁢      ethane        =                                        [            CO            ]                    /          2                +                              [                          CO              2                        ]                    /          2                +                  [                                    C              2                        ⁢                          H              4                                ]                +                  [                                    CH              3                        ⁢            COOH                    ]                                                  [            CO            ]                    /          2                +                              [                          CO              2                        ]                    /          2                +                  [                                    C              2                        ⁢                          H              4                                ]                +                  [                                    C              2                        ⁢                          H              6                                ]                +                  [                                    CH              3                        ⁢            COOH                    ]                                selectivity      ⁢                          ⁢              (        efficiency        )            ⁢                          ⁢      to      ⁢                          ⁢      ethylene      ⁢                          ⁢      and      ⁢                          ⁢      acetic      ⁢                          ⁢      acid        =                            [                                    C              2                        ⁢                          H              4                                ]                +                  [                                    CH              3                        ⁢            COOH                    ]                                                  [            CO            ]                    /          2                +                              [                          CO              2                        ]                    /          2                +                  [                                    C              2                        ⁢                          H              4                                ]                +                  [                                    C              2                        ⁢                          H              6                                ]                +                  [                                    CH              3                        ⁢            COOH                    ]                    
One application of a catalytic ethane to ethylene and acetic acid process would be as a front end process for commercial vinyl acetate monomer (VAM) synthesis. The reaction of acetic acid with ethylene (acetoxylation) is the dominant route to vinyl acetate today. Because current vinyl acetate process technology is mature, accomplishing significant improvements has become increasingly difficult. A reduction in feedstock costs would lead to cost-savings in the production of VAM. The use of ethane and oxygen as starting feedstock would represent a significant savings in raw material cost over the currently-used ethylene and acetic acid.
It would be desirable to have a process which reacts ethane with oxygen over a catalyst to selectively coproduce a product stream comprising ethylene and acetic acid, which product stream could be used in VAM production.